The present invention generally relates to the preparation or testing of sample substances contained in vessels in which stirring devices or other instruments operate. More particularly, the present invention relates to the centering and alignment of such vessels with respect to the stirring device.
In the pharmaceutical industry, the stirring or agitation of sample drugs or other substances in vessels is an important step in sample preparation procedures. Examples of such procedures include those performed for the purpose of testing and analyzing the rate at which doses release from pharmaceutical products, such as tablets or capsules, under controlled conditions. The procedural steps, test duration, dissolution medium, and apparatus employed in dissolution tests typically must comply with established, well-recognized guidelines, such as those promulgated by United States Pharmacopeia (USP), in order for the test to be accepted as valid for the specific substance tested.
The apparatus utilized for carrying out dissolution testing typically includes a vessel plate having an array of apertures into which test vessels are mounted. When the procedure calls for heating the media contained in the vessels, a water bath is often provided underneath the vessel plate such that each vessel is at least partially immersed in the water bath to enable heat transfer from the heated bath to the vessel media. In one exemplary type of test configuration (e.g., USP-NF Apparatus 1), a cylindrical basket is attached to a metallic drive shaft and a pharmaceutical sample is loaded into the basket. One shaft and basket combination is manually or automatically lowered into each test vessel mounted on the vessel plate, and the shaft and basket are caused to rotate. In another type of test configuration (e.g., USP-NF Apparatus 2), a blade-type paddle is attached to each shaft, and the pharmaceutical sample is dropped into each vessel such that it falls to the bottom of the vessel. When proceeding in accordance with the general requirements of Section  less than 711 greater than (Dissolution) of USP24-NF19, each shaft must be positioned in its respective vessel so that its axis is not more than 2 mm at any point from the vertical axis of the vessel.
It is therefore an important criterion in certain uses of vessels in which shafts operate that the vessel, and especially its inner surfaces, be aligned concentrically with respect to the shaft, and various approaches have heretofore been taken to assist in meeting this criterion.
One approach is disclosed in U.S. Pat. No. 5,403,090 to Hofer et al., in which at least two embodiments of a vessel aligning structure are provided to lock a standard USP dissolution test vessel into a stable, centered position in a vessel plate relative to a stirring shaft. The vessel is extended through one of the apertures of the vessel plate such that the flanged section of the vessel rests on the top of the vessel plate.
In one embodiment disclosed in U.S. Pat. No. 5,403,090, the vessel aligning structure includes an annular ring having a tapered cylindrical section depending downwardly against the inner surface of the vessel, and an annular gasket surrounding the annular ring. When the vessel aligning structure is pressed onto the vessel, the annular gasket is compressed between the vessel aligning structure and the flanged section of the vessel. A mounting receptacle is secured to the vessel plate adjacent to each aperture of the vessel plate. The vessel aligning structure further includes a horizontal bracket arm which slides into the mounting receptacle and is secured by a wing nut and associated threaded stud. The bracket arm also supports the mounting assembly for the motor and stirring shaft associated with that particular vessel location of the vessel plate.
In another embodiment disclosed in U.S. Pat. No. 5,403,090, the vessel aligning structure includes a plurality of mounting blocks secured to the vessel plate. One mounting block is positioned over each aperture of the vessel plate. Each mounting block includes a tapered cylindrical section depending downwardly against the inner surface of the vessel. The mounting block has two alignment bores which fit onto corresponding alignment pegs protruding upwardly from the vessel plate.
Another approach to vessel alignment is disclosed in U.S. Pat. No. 5,589,649 to Brinker et al, in which each aperture of a vessel plate is provided with three alignment fixtures circumferentially spaced in 120 degree intervals around the aperture. Each alignment fixture includes two semi-rigid alignment arms or prongs extending into the area above the aperture. The flanged section of the vessel rests on top of the alignment arms, such that each pair of alignment arms contact the outer surface of the vessel and the vessel is thereby supported by the alignment fixtures. The alignment arms are described as exerting compressive or xe2x80x9csymmetrical springxe2x80x9d forces that tend to center the vessel within the aperture of the vessel plate in which the vessel is installed in order to align the vessel with respect to a stirring element.
Many current vessel centering systems require an unacceptably large footprint around the vessels of a dissolution testing apparatus. As acknowledged by those skilled in the art, a vessel centering system that takes up less area would permit the design of a smaller overall apparatus. The use of a smaller apparatus would be highly desirable in view of the costs associated with building and maintaining pharmaceutical laboratory space.
In addition, current vessel centering systems require the manipulation of two or more components to account for the often poor and/or inconsistent manufacturing tolerances observed in the wall thickness of the extruded glass tubing from which vessels are formed and in the vessel manufacturing process itself. As noted in the publication xe2x80x9cDissolution Discussion Group(copyright),xe2x80x9d Vol. 1, Section 29.2 (VanKel Technology Group, 1999), glass vessels can be made by hand from large-bore glass tubing. The glass tubing is placed in a rotating device similar to a lathe, heat is applied, and the tubing is separated and sealed to form a hemispheric or other shaped bottom section. Heat is continually applied while the vessel is blown into the desired shape. This labor-intensive process can result in dimensional irregularities in the finished glass product. While plastic vessels are manufactured with better tolerances since they are fashioned from molds, plastic vessels are generally less desirable in many applications due to drug affinity with the surface and slower heat-up rate. Accordingly, there presently exists a need for developing a vessel centering system that adequately addresses the poor tolerance issue.
It is believed that a continuing need exists for practical and effective solutions to providing a vessel centering system. The present invention is provided to address these and other problems associated with the centering and alignment of vessels.
The present invention generally provides a vessel centering or alignment system which establishes and maintains a high degree of concentricity between the inner surfaces of a vessel and its associated shaft. The invention finds advantageous utility in any application in which concentricity is desired as between a vessel and a shaft or other elongate instrument extended into and operating within the vessel. The invention is particularly useful in connection with a sample handling or dissolution apparatus in which one or more vessels are to be installed onto or into some type of a vessel plate or rack. The invention is broadly characterized as providing a vessel which has a structurally distinct, locking flanged section.
According to one embodiment of the present invention, a vessel is adapted for improved centering with respect to a spindle when such vessel is installed in a vessel plate. The vessel comprises a vessel wall, an annular, spacer member, and a fastening or locking element. The vessel wall includes an outer surface and a vessel groove formed on a circumference of the vessel outer surface. The spacer member is fitted in the vessel groove and extends outwardly with respect to the vessel wall, terminating at a first lateral end surface and a second lateral end surface. The fastening element engages the spacer member near the first and second lateral end surfaces.
According to another embodiment of the present invention, the spacer member includes an outer surface, a first lateral end surface, a second lateral end surface, a first tangential bore, and a second tangential bore. The first tangential bore extends from a first outer aperture of the spacer member outer surface to a first inner aperture of the first lateral end surface. The second tangential bore extends from a second outer aperture of the spacer member outer surface to a second inner aperture of the second lateral end surface. The first and second lateral end surfaces define a gap therebetween. The first and second tangential bores extend along a line generally tangential to a curvature of the spacer member. The fastening element is disposed in the first and second tangential bores. The fastening element extends through the first inner aperture, across the gap, and through the second inner aperture, such that the fastening element is movable along the generally tangential line of the first and second tangential bores to engage the spacer member and tighten or lock the spacer member in the vessel groove.
According to yet another embodiment of the present invention, a vessel centering system comprises a vessel, an annular, spacer member, a fastening element, and an elastometric component. The vessel includes an outer surface and a vessel groove formed on a circumference of the vessel outer surface. The spacer member is fitted in the vessel groove and extends outwardly with respect to the vessel, terminating at first and second lateral end surfaces. The first and second lateral end surfaces define a gap therebetween. The spacer member includes a tangential bore and an annular groove. The tangential bore extends along a line generally tangential to a curvature of the spacer member. The fastening element is disposed in the tangential bore in engagement with the spacer member and extends across the gap. The elastometric component is disposed in the annular groove.
According to a further embodiment of the present invention, a vessel centering system comprises a vessel including an outer surface and a vessel groove formed on a circumference of the vessel outer surface, an annular, C-shaped ring member fitted in the vessel groove and extending outwardly with respect to the vessel, and means for tightening the ring member against the vessel groove.
According to an additional embodiment of the present invention, a vessel centering system includes a radial extension element disposed in contact with a ring member fitted to a precision groove cut along an outer circumference of a vessel.
According to yet another embodiment of the present invention, a plurality of biased bearings are substituted for the elastometric component.
According to a still further embodiment of the present invention, the vessel centering system comprises means for presenting a vessel alignment surface for the vessel centering system.
According to an additional embodiment of the present invention, a vessel centering system comprises a vessel plate, a vessel, an annular, spacer member, and a mechanical contact element. The vessel plate includes a vessel plate aperture. The vessel plate aperture includes a first edge and a second edge which cooperatively define an annular shoulder. The vessel extends through the Vessel plate aperture, and includes an outer surface and a vessel groove formed on a circumference of the vessel outer surface. The spacer member is fitted in the vessel groove and disposed on the first edge of the vessel plate aperture. The spacer member terminates at a first lateral end surface and a second lateral end surface. The mechanical contact element is disposed in engagement with the spacer member at the first and second lateral end surfaces.
The present invention also provides a method for aligning a vessel concentrically with respect to a shaft extending into the vessel, wherein an annular member is fitted in a groove formed around an outer surface of a flangeless vessel body, thereby forming a multi-piece flanged vessel. The ring member is locked or tightened in the vessel groove by utilizing a fastening element engaging the ring member.
The present invention further provides a method for assembling a vessel centering system. A circumferential groove is formed on an outer surface of a flangeless vessel body. An annular, spacer member can be formed such that the spacer member terminates at a first lateral end surface and a second lateral end surface, with the first and second lateral end surfaces defining a gap therebetween. A tangential bore is formed in the spacer member such that the tangential bore extends along a line generally tangential to a curvature of the spacer member and includes two bore sections opposing each other across the gap of the spacer member. A fastening element is provided and is adapted to engage the spacer member at the tangential bore. The spacer member is fitted in the vessel groove to form a multi-piece flanged vessel. The spacer member is secured in the vessel groove by adjusting a position of the fastening element with respect to the tangential bore.
It is therefore an object of the present invention to provide a vessel centering system adapted to easily and quickly achieve concentricity as between the inner surfaces of a vessel and a stirring element or other spindle or shaft-type instrument inserted into the vessel.
It is another object of the present invention to provide a multi-piece flanged vessel wherein the flanged section is a separate, removable structural component.
It is a further object of the present invention to provide a flanged vessel wherein the flanged portion can be locked onto the vessel wall or removed therefrom.
It is yet another object of the present invention to provide a vessel adapted for improved installation with a vessel plate, such as a vessel plate typically provided with a liquid handling apparatus or dissolution testing apparatus.